The present invention relates to a rocking apparatus for attaching a given member to another member in such a manner that the given member can rock. More particularly, the present invention relates to improvement of a rocking apparatus for supporting a first supported member on a second supporting member so as to be capable of oscillation in such a manner that a seat is attached to a leg portion in a chair so that the seat can tilt for example, and a self-holding mechanism of a locking mechanism for locking the supported member at an arbitrary position or inclination in connection with the rocking apparatus.
An example of a rocking apparatus for supporting a first supported member with respect to a second supporting member in such manner that the supported member can rock, is a chair such as shown in FIGS. 19 and 20. The rocking apparatus 201 is provided with: a seat bearing member 203 supported on a leg 202; a supporting shaft 204 rotatably attached to the front side of the seat bearing member 203 with its longitudinal direction corresponding to the width direction of the chair; brackets 206, 206 fixed at both ends of the supporting shaft 204 in order to support a seat 205; a rocking plate 207 fixed at the central portion of the supporting shaft 204; a reaction force imparting mechanism 208 formed of a helical compression spring for upwardly pushing the rocking plate 207; and a lock mechanism (not shown) for fixing the seat 205 and a backrest 209 with an arbitrary inclination. Here, there can be adopted as the lock mechanism various kinds of mechanisms such that a gas spring is provided between the seat bearing member 203 and the bracket 206, a shaft member pierces through the bracket 206 and the seat bearing member 203 so that they can be fixed, a lock member of the seat bearing member 203 is engaged with a gear member fixed to the bracket 206 for fixing, or a plurality of clutch plates are fixed and superimposed respectively on the bracket 206 and the seat bearing member 203 so that they can be fixed by fastening the respective clutch plates. In this chair, the seat 205 and the backrest 209 can rock by unlocking the lock mechanism. On the other hand, the seat 205 and the backrest 209 can be locked at a desired angle by locking the lock mechanism.
Further, as shown in FIG. 21, there is another rocking apparatus in which a torsion bar 110 is adopted as a reaction force imparting mechanism. In case of this rocking apparatus 101, a central portion of the torsion bar 110 is fixed to the seat bearing member 103 attached to the leg 102 while the brackets 106, 106 are fixed to the both ends of the torsion bar 110 and, when a user applies his/her weight on a backrest integrated with the seat, the seat tilts backwards the brackets 106, 106 twisting the torsion bar 110. As a result, the seat and the backrest tilt backwards while receiving the reaction force of the torsion bar 110 when the load is applied in the rear direction, and they are returned to their original positions by the torsion bar 110 when this load is no longer applied, thereby performing the rocking operation.
In each rocking apparatus described above, however, the seat is supported on only the brackets provided on the both sides, which requires large brackets that are long in the front-and-back direction. This results in deterioration in the appearance of the chair and in restriction in design. In addition, since the large brackets are necessary, a decrease in a number of parts is difficult and assembling work of the chair is complicated, thereby making it hard to reduce the manufacturing cost.
There is still another chair having a rocking apparatus provided with a lock mechanism with which the seat and the backrest can be fixed at a given angle. For example, the rocking apparatus 101 shown in FIG. 22 includes: a front seat frame 104 fixed to the leg 106; a rear seat frame 102 which can rock with respect to the leg 106; the reaction force imparting mechanism (not shown) for imparting a force for returning the rear seat frame 102 to its original position; and the lock mechanism 107 formed of a gas spring which can lock with the rear seat frame 102 being inclined (see Japanese patent laid-open publication No. Hei 4-193108). In this chair, the seat 103 and the backrest 105 can rock by setting the lock mechanism 107 to the unlocking mode. On the other hand, when the lock mechanism 107 enters the locking mode, the seat 103 and the backrest 105 can be locked while maintaining their inclination.
In this rocking apparatus, however, when the lock mechanism is switched to the unlocking mode, the locked state of the seat and the backrest is immediately canceled so that they can be rocked. Accordingly, when the lock mechanism is set in the locking mode with the seat and the backrest being inclined and no one is sitting in the chair, the reaction force caused by the reaction force imparting mechanism may suddenly spring up the seat and the backrest by switching the lock mechanism from the locking mode to the unlocking mode.